Treating electrodes



Patented Juli 19, 1932 I UNITED s'rATEs,

PATENT-OFFICE mm m. rronrnn AND LOUIS a. wean, on mnnm, MICHIGAN, Assrenoas ro man now onnmcnn column, or" mnmnnmomoA-n, A oonronnrron or monrean I rans'rme nnncrnonns 1T0 Drawing.

. The present invention is concerned with the treating of porous electrodes to make same less porous and more durable, andis applicable to the treatment of carbon or 5 graphitized carbon electrodes or electrodes of graphitic material to be used in the electro ysis of aqueous baths, e. g. electrolysis of a sodium chloride solution for the production of caustic soda and chlorine. Various methods of treating such electrodes have been proposed, among which may be mentioned the impregnation with an oil, a wax, or other suitable material. Among the pur oses of such impregnation is the filling of the pores to prevent or diminish the diffusionof electrolyte into or through the electrode, whereby excessive wear due to oxida t1on is eliminated, and when a bi-polar elec- :trodeis used the intermixture of anodic and cathodic products is controlled, while corrosion of contacts is controlled when a unipolar electrode is used. With'such treatment the life of the ele'btrode, as an anode, is materially increased. i We have invented an improvement in th treatment of electrodes, particularly adapted to the treatment of carbon or raphitized carbon electrodes used in the pro notion of caustic alkaliand zehlorine, whereby the advantagessher etdfore gained by impregnation are '"Tharkedlyincreased.

To the accomplishment of the foregoing and related ends, the invention then consists of the steps hereinafter fully described and particularly pointed out in' the claims, the

ollowing description setting'forth' in detail one mode of carrying out the invention, such disclosed mode illustrating, however, but one of various ways in which the principle of the invention may be used.

. Our method of treatment comprises, briefly, the impregnation of a carbonor .graphitized carbon electrode with oil, such as'China wood oil, followed'by the exosure of the so impregnated electrode to su stanof the electrodes.

Application filed June 16, 1930; Serial in. 461,883.

tially dry chlorine gas. In carryin out our improved method we charge the e ectrodes into a vessel which may be evacuated and which is also adapted to withstand internal duced into thevessel so that the electrodes sure is applied to force the oil into the pores After the electrodes have been thoroughly impregnated, the oil is drawn ofi and a vacuum is again put upon the container to assist in the drainage of excess oil. The vacuum is then released and the impregnated electrodes are removed and charged into a vessel and therein subjected to the action of a current of substantially dry chlorine gas. After a sufiicient period of exposure the gas is shut off, and the electrodes removed from the vessel. A sticky coatin is formed upon the surface of the electro es, which hardens when exposed to the air, and in order to clean the surface the electrodes may be scraped, wire brushed, buffed or treated with an alkaline bath. The aforesaid treatment may be repeated one or more times, if required, to produce the desired degree of impermeability in the treatedcelecrode. The final result is to produce a chlorinatedoil-impregnated electrode which we find by use in the electrolysisof a salt solu-' tion for the production of caustic soda and chlorine to have a markedly longer useful life thana likejelectrode which has been similarly impregnated-but not chlorinated. I

We 'find that the temperature of impregnation,using China wood oil, will advisedly be kept belowthe temperatureof polymeriza-. tion thereof. In practice, we use a temperar ture within the range of 30 to?'75 C. We

find that' the duration ofthe pressure sta in' the oil impregnation step may be in t e are completely submerged therein, and presneighborhood of 4 to 8 hours, the exact time varying with the size and specificstructural characteristics of the material being impregso desired.

nated. A pressure of approximately 90 pounds has been found satisfactory, although a higher or lower pressure may be used, if

The chlorination of the oil-impregnated electrodes in an aqueous salt solution under Example 100 pounds Acheson graphitized carbon electrodes were charged into a cylindrical impregnator which was then closed and evacuated by means of a pump tov a pressure of about -1 pound per square inch absolute pressure and held at that pressure for about one hour. While the connection to the vacuum pump was still open, China'wood oil was admitted and after the oil had covered the electrodes the vacuum connectionwas closed and more oilwas' forced in under a pressure of about 90pounds. This oil pressure was i The vessel was closed and the chlorine was passed through it for about 40 days wherethen held at approximately 90 pounds per square inch gauge for about 8 hours. The oil-was then drawn off and the impregnator again evacuated to an absolute pressure of about 1 pound. Upon releasing the vacuum the excess oil which had been drained away froin the electrodes was removed. The particular lot of electrodes treated. took up approximately 8 per cent. by weight of oil relative to the weight of the untreated electrodes. The so impregnated electrodes were then transferred to a chlorinating vessel comprising through which dry chlorine was passlng so that a stream of the chlorine could be also bypassed through the chlorination vessel. The chlorine had been dried over sulphuric acid.

upon the chlorine supplywas out 01f andthe' electrodes removed. After chlorination the electrodes were covered with a sticky film which was found to harden upon exposure to air. Some'of the electrodes were scraped to remove the coating, others were washed with a solution of caustic cell liquor containing about 10 per cent. NaOH to remove the surface-coating. The so treated and cleaned electrodes were employed in electrolytic chlorine cells of the bi-polar type alongside of other cells having like electrodes which hadalso been impregnated with Chinawood oil,

a cylinder connected to a pipe line but had not been chlorinated. The cells containing the chlorinated electrodes gave superior service and the life of the chlorine-treated electrodes was found to be ap roximatel 50 per cent. greater than that o the unch orinated ones.

chlorinated electrode greater, but there was experienced far less trouble in the cell operation using them. The cells containing the merely impregnated electrodes developed diaphragm troubles due. to oil oozing cut of the electrodes and fouling the diaphragm. Such action was substantially absent in the cells using the prechlorinated electrodes.

, The length of time of treatment of the oilimpregnated electrodes may be materially varied from the eriod given in the above example. The p ysical properties of the electrodes, i. e. shape, size, porosity, etc., and

a the particular type of oil or mixture of oils used, largely determine the time of exposure to the ch orine gas to effect a desired result. In general, a lengthening of the time of chlorination, correspondingly increases the useful life of the electrodes in service. By

Not only was the service life of the pro-- scraping or cleaning the oil-impregnated I electrodes after artial chlorinationand subsequently repeatlng the'chlorination in some cases a superior result maybe obtained.

We have illustrated the use'of' our invention employing China wood oil, but we wish it distinctly understood that other dryingoils, such as linseed oil, cottonseed oil, or a mixture-of oils comprising the same which by reaction with chlorine will more edective ly close the ores in the electrode, vmay be employed. compounds or oils mixed w1th diluents. or with chlorination accelerating agents are also suitable to be used.

Other modes of applying the principle of our invention may em loyed instead of the one explained, change ing made as regards the method herein disclosed provided the step or steps stated by any of the following claims or the equivalent of such stated step or steps be employed. a

We therefore particularly point out and distinctly claim as our invent on graphitized carbon electrodes, the steps which consist in impre ating said electrodes with a drying oil an then exposing the so impregnated electrodes to substantially dry chlorine gas.

2. In amethod of treating carbon orils containing unsaturated;

*1. In a method of treating carbon oring air from the pores thereo ,impregnating the same with China. wood oil under 'superatmospheric proximately etween 30 and 75 0., draining off surplus oil and subjecting the lmpre 7 pregnatin the same with a 0 pressure, raining ofi surplus and sub ecting the impregnated electrodes to the 9.0-.

tion of substantially dry chlorine gas.

f1. The method of treating carbon or graphitized electrodes which com rises evacuatressure at a temperature apnated electrodes to the action of substanti y dry chlorine gas. Signed by us this 13th day of June 1930.

RALPH M. HUNTER. LOUIS E. WARD.

oil under I 

